I. Field of the Invention
The present invention relates to communications systems. More particularly, the present invention relates to a novel and improved for processing data for transmission in a high speed spread spectrum communications system.
II. Description of the Related Art
The present invention is concerned with multiple users sharing a communications resource such as in a cellular CDMA system. The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication techniques, such as time division multiple access (TDMA), frequency division multiple access (FDMA) and AM modulation schemes such as amplitude companded single sideband (ACSSB) are known in the art. However, the spread spectrum modulation technique of CDMA has significant advantages over these other modulation techniques for multiple access communication systems. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled xe2x80x9cSPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERSxe2x80x9d, assigned to the assignee of the present invention and incorporated by reference herein. The use of CDMA techniques in a multiple access communication system is further disclosed in U.S. Pat. No. 5,103,459, entitled xe2x80x9cSYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEMxe2x80x9d, assigned to the assignee of the present invention and incorporated by reference herein.
CDMA by its inherent nature of being a wideband signal offers a form of frequency diversity by spreading the signal energy over a wide bandwidth. Therefore, frequency selective fading affects only a small part of the CDMA signal bandwidth. Path diversity is obtained by exploiting the multipath environment through spread spectrum processing by allowing a signal arriving with different propagation delays to be received and processed separately. Furthermore, space or path diversity is obtained by providing multiple signal paths through simultaneous links between a mobile user and two or more base stations. Examples of the utilization of path diversity are illustrated in U.S. Pat. No. 5,109,390 entitled xe2x80x9cDIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEMxe2x80x9d, and U.S. Pat. No. 5,101,501 entitled xe2x80x9cSOFT HANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEMxe2x80x9d, both assigned to the assignee of the present invention and incorporated by reference herein.
An additional technique that may be used to increase the efficiency of the allocation of the communication resource is to allow the users of the resource to provide data at varying rates thereby using only the minimum amount of the communication resource to meet their service needs. An example of variable rate data source is a variable rate vocoder which is detailed in U.S. Pat. No. 5,414,796, entitled xe2x80x9cVARIABLE RATE VOCODER,xe2x80x9d assigned to the assignee of the present invention and incorporated herein by reference. Since speech inherently contains periods of silence, i.e. pauses, the amount of data required to represent these periods can be reduced. Variable rate vocoding most effectively exploits this fact by reducing the data rate for these silent periods.
A variable rate speech encoder provides speech data at full rate when the talker is actively speaking, thus using the full capacity of the transmission frames. When a variable rate speech coder is providing speech data at a less than maximum rate, there is excess capacity in the transmission frames. A method for transmitting additional data in transmission frames of a fixed size, wherein the data source is providing data at a variable rate is described in detail in U.S. Pat. No. 5,504,773, entitled xe2x80x9cMETHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSIONxe2x80x9d, assigned to the assignee of the present invention and incorporated by reference herein. In the above mentioned patent application a method and apparatus is disclosed for combining data of differing types from different sources in a data packet for transmission.
Recently, the transmission of digital data over wireless networks has become increasingly important. For example the transmission of image, video or other digital data over wireless networks has become of great importance. Digital networks were designed to provide optimal performance for the transmission of speech data. Other forms of digital data require significantly higher data rates for proper performance.
One method of providing high speed forward link data in a spread spectrum communication system is to provide multiple orthogonal channels to carry the data to a single high speed user. A method for transmitting high speed digital data on multiple orthogonal channels is described in detail in copending U.S. patent application Ser. No. 08/431,180, entitled xe2x80x9cMETHOD AND APPARATUS FOR PROVIDING VARIABLE RATE DATA IN A COMMUNICATION SYSTEM USING STATISTICAL MULTIPLEXINGxe2x80x9d, filed Apr. 28, 1995, which is assigned to the assignee of the present invention and incorporated by reference herein.
One aspect of transmitting high speed variable rate data is that the remote station must demodulate multiple channels. Demodulating multiple channels uses battery power which is important in mobile applications. One method of reducing the unnecessary demodulation of data channels, when no high speed data is present, is to schedule the use of the additional channels to alert the remote station of forthcoming high speed data. A method and apparatus for scheduling the high speed transmissions is described in detail in copending U.S. patent application Ser. No. 08/656,649, entitled xe2x80x9cMETHOD AND APPARATUS FOR PROVIDING RATE SCHEDULED DATA IN A SPREAD SPECTRUM COMMUNICATION SYSTEMxe2x80x9d, filed May 31, 1996, which is assigned to the assignee of the present invention and is incorporated by reference herein.
An alternative to transmitting data on a plurality of supplemental channels is to transmit high speed data on a single supplemental channel capable of carrying higher data rates than a single common channel. These high data rate channels can be provided by combining the orthogonal modulation of a plurality of traffic channels.
One method for transmitting high speed data on the reverse link is to generate a plurality of subchannels at the remote station wherein each subchannel is distinguished from the other subchannels by means of an orthogonal coding. A method of providing high speed data on the reverse link using a plurality of subchannels is described in detail in copending U.S. patent application Ser. No. 08/654,443, filed May 28, 1996, entitled xe2x80x9cHIGH DATA RATE CDMA WIRELESS COMMUNICATION SYSTEMxe2x80x9d and in copending U.S. patent application Ser. No. 08/660,438, filed Jun. 7, 1996, entitled xe2x80x9cREDUCED PEAK TO AVERAGE TRANSMIT POWER HIGH DATA RATE CDMA WIRELESS COMMUNICATION SYSTEMxe2x80x9d, both of which are assigned to the assignee of the present invention and incorporated by reference herein.
The present invention is a novel and improved method and apparatus for transmitting high speed digital data in a spread spectrum communications system. In particular, the present invention provides methods for transmitting forward link and reverse link high speed digital data. For both forward link and reverse link transmissions, the present invention describes a method for processing the data for transmission in a 1.2288 Mcps band and in a 3.6268 Mcps band. In addition, the present invention describes a method for transmitting forward link and reverse link data of both rate set 1 digital data and rate set 2 digital data. Rate set 1 digital data comprises variable rate data at rates defined as Mux Option 1 in the IS-95 standard. Rate set 2 digital data comprises variable rate data at rates defined as Mux Option 2 in the appendix to the IS-95 standard. In addition the present invention describes methods of transmitting the data for applications using packet switched technology and circuit switched technology.